MNG-03 PD-L1 EXPRESSION, PATIENT PROGNOSIS AND INITIAL WHO GRADE IN GRADE II/III MENINGIOMA

The optimal treatment for grade II/III meningioma is operation with or without radiation therapy. However, their natural course is sometimes aggressive with high recurrent rate. There is no effective treatment other than operation and radiation therapy, therefore, a new therapeutic strategy for grade II/III meningioma is urgently required.PD-1 and PD-L1 play important roles as immune-checkpoint mediators within tumor microenvironment and the antibodies to these molecules are now approved for the treatment of various kinds of cancers. In Japan, anti-PD-1 antibody and anti-CTLA-4 antibody are approved for unresectable melanoma or advanced / recurrent non-small cell lung cancer and their high effectiveness has been reported. We investigated the expression of PD-L1 (clone:28-8) in 51 cases of grade II/III meningioma by immunohistochemistry and analyzed the relationship between the expression with overall survival, progression free survival and initial WHO grade. For now, we have evaluated 25 cases of PD-L1 immunohistochemistry and PD-L1 showed positivity in 15 cases. There is no correlation observed between PD-L1 expression and patients’ prognosis. Although it does not reach a significant difference, the WHO grade at the time of initial operation tends to be high in those with high PD-L1 staining rate.Similar studies that were previously reported did not use antibodies targeting clone 28-8, which was used as a companion diagnosis for nivolumab administration, but “Correlation between PD-L1 expression and WHO grade”, or “PD-L1 expression is an independent prognostic factor” have been reported. In our investigation, which was using antibodies for companion diagnosis, PD-L1 was positive in more than half of Grade II / III meningiomas and it also related to WHO grade. These results suggest the possibility that tumor immune evasion mechanisms are also working in meningiomas. At the conference, we will report it with the specific data from all cases with a literature review.